Methyl 3,7-dimethyl-7-hydroxyoctylideneanthranilate is a Schiff base compound, prepared from hydroxycitronellal (3,7-dimethyl-7-hydroxyoctanal) and methyl anthranilate. Hydroxycitronellal used as a starting material for the production of this compound is also a synthetic perfume and has chiefly been available in the form of either d-hydroxycitronellal that is obtained by hydrolysis of a sulfurous acid adduct of d-citronellal derived from citronella oil, or dl-hydroxycitronellal that is prepared from dl-citronellal which is prepared from myrcene. In other words, an l-form of hydroxycitronellal has seldom been used (see O. Okuda, Koryo Kagaku Soran (Review of Perfume Chemistry), p. 753, Hirokawa Publishing Company, 1968).
Therefore, methyl 3,7-dimethyl-7-hydroxyoctylideneanthranilate has generally been known only in its d- or dl-form. Being a classical fragrance raw material having an orange flower note, methyl 3,7-dimethyl-7-hydroxyoctylideneanthranilate has been recognized as an indispensable aroma chemical that is compounded for manufacturing perfumes within the class of floral family (see Steffen and Arctander, Perfume and Flavor Chemicals Monograph, No. 1735 (1969)). However, no case has been reported of success in isolating the l-form of methyl 3,7-dimethyl-7-hydroxyoctylideneanthranilate or in identifying its fragrance and properties. There has also been no report on the characteristics or safety features of this compound as a perfume.
With the recent concern over the safety of perfumes, there is a global need to create perfumes that present much less hazard to human health. In this connection, it has been reported that hydroxycitronellal which is not only a synthetic perfume per se but also used as a starting material for the production of methyl 3,7-dimethyl-7-hydroxyoctylideneanthranilate has a potential for causing dermatitis when it is used in a cream base (see H. Nakayama, Perfume Allergy and Patch Test in Perfume Chemistry Books, No. 1, Fragrance Journal Publishing Company, p. 78 (1983)). This suggests the possibility that the conventionally used methyl 3,7-dimethyl-7-hydroxyoctylideneanthranilate also has a potential for causing contact allergy. If so, this compound cannot be used in the preparation of perfumes of either the citrus or neroli family. Therefore, development of a substitute that has the closest resemblance to the conventional methyl 3,7-dimethyl-7-hydroxyoctylideneanthranilate not only in terms of fragrance but also with respect to other properties such as solubility is strongly desired.
The present inventors synthesized various aldehyde compounds, reacted them with methyl anthranilate to prepare Schiff bases, and investigated the safety and other characteristics of these Schiff bases used as perfumes. During the course of these studies, the present inventors established a method of synthesizing l-hydroxycitronellal (see Japanese Patent Application (OPI) No. 4748/1983) with the attendant finding that the l-form of hydroxycitronellal has a very low level of allergenicity as compared with its d-form. (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".)
In addition to the note of fragrance and solubility of the Schiff bases, the present inventors investigated their potential to cause contact allergy (or sensitization) by conducting an allergenicity test on guinea pigs with a view to searching for a substitute that is safer to use and which yet provides a note of fragrance that is not much different from those of the conventional isomers of hydroxycitronellal. As a result, the present inventors found that only methyl 3,7-dimethyl-7-hydroxyoctylideneanthranilate is acceptable because of its balanced properties, i.e., very low sensitizing potential, note for fragrance that is not much different from those of other isomeric forms of hydroxycitronellal, less irritating odor, cleanness, and an added green note. The present invention has been accomplished on the basis of this finding.